1. Field of the Invention
The present invention relates to the manufacture of disk storage devices. More particularly, the invention is directed to an apparatus and method for vibration control between multiple actuators as are commonly used in such storage devices.
2. Description of the Background Art
Disk storage devices are well known in the industry today. Many versions exist, with the most widely used probably being magnetic disk storage devices termed xe2x80x9chard drivesxe2x80x9d or xe2x80x9cfixed disk drives.xe2x80x9d In these, one or more disks coated with a magnetic storage media are rotated and data is written to and read from the media with read/write heads pivotally mounted on actuator assemblies. Optical and other types of disk storage devices are also known or possible, and it should clearly be appreciated that the present invention may improve many embodiments of these as well, but for exemplary purposes the present discussion will primarily be directed to magnetic disk storage devices.
Modern disk storage devices often have a number of competing design goals. Without limitation, these may include reliability, accuracy, small size, high storage density, and high data access and transfer speeds. A key portion of a disk storage device may thus be the pivot or actuator assembly or assemblies which position read/write heads over the storage media. Traditionally, single pivot assemblies have primarily been used, but multiple pivot assembly systems are also known, and in seeking to reach various of the competing design goals the industry is now turning to multiple pivot assembly systems, particularly dual pivot assembly systems.
Unfortunately, aside from the obvious additional mechanical complexity, multiple pivotal actuator assemblies introduce a number of additional problems for the designers of disk storage devices. Of present interest are how they create, transfer, and are effected by vibration. Before turning to a discussion of this, however, a brief summary of the state of the prior art may by useful.
Vibration is a problem even in single pivot assembly systems. U.S. Pat. No. 5,930,071 by Black teaches a rubber-like material to dampen vibrations at the bearings and the shaft at which the single actuator assembly pivots. Japanese Pat. No. 2-139772 by Hidehiro teaches a single pivot assembly wherein the shaft has an elastic core into which a screw extends to hold the shaft in place. And Japanese Pat. No. 1-048271 by Hiroshi teaches a vibo-elastic material on an outer circumference to reduce vibration from the device housing effecting a single carriage.
In notable contrast, when the industry has turned to dual pivot assembly systems it has essentially ignored the problem vibration control, or worked around it using basic design methodologies not germane to this discussion. U.S. Pat. No. 4,544,972 by Kogure et al. and Japanese Pat. No. 62-78783 also by Kogure teach dual actuator assemblies without vibration dampening or isolation. U.S. Pat. No. 5,761,007 by Price et al. also teaches multiple actuators, and it even uses a elastometric sleeve. But this sleeve is merely part of a crash stop against which an actuator stops its pivotal motion in one direction, rather than any manner of vibration control. Thus multiple pivot assembly systems with vibrations control remain something unknown in the art.
As described, traditional multiple actuator designs have a dual pivot with a single shaft. Unfortunately, the conventional single shaft used provides a transmission path for vibration to travel between the respective actuators. Since the use of multiple actuators is generally a straight forward extension of the principles for dual actuators, the dual actuator case will primarily be discussed herein.
FIG. 1 (background art) is a side broken view of bearing assemblies for dual actuators mounted on a single shaft, as might be found in the prior art. A common shaft 1 is provided which is mounted within a disk storage device housing (not shown). Respective bearing assemblies 2, one per actuator, are mounted on the common shaft 1, typically spaced apart by a separation maintainer 3 (e.g., a spacer or bushing) as shown in FIG. 1.
The bearing assemblies 2 each include two bearings 4 which are mounted in a sleeve 5 of the actuator (also not otherwise shown). Specifically, in the embodiment shown in FIG. 1, the bearings 4 include inner races 6 and outer races 7. The bearings 4 depicted in FIG. 1 are ball-type bearings, but roller-types and, at least in theory, other types of bearings may also be employed.
As can be seen in FIG. 1, the outer races 7 of the bearings 4 are fixedly mounted in the sleeves 5 of the respective actuators, and the inner races 6 of the bearings 4 are fixedly mounted on the common shaft 1. FIG. 1 also depicts one common arrangement, wherein the inner race 6 of the lower-most bearing 4 in the bottom bearing assembly 2 abuts against a base flange 8 of the common shaft 1. The separation maintainer 3 then abuts against the top-most inner race 6 of the bottom bearing assembly 2 as well as against the lower-most inner race 6 of the upper bearing assembly 2. In this manner, when the media disk in a disk storage device is oriented to revolve in a horizontal plane, the actuators are horizontally pivotally mounted and vertically fixedly mounted on the common shaft 1.
Unfortunately, this arrangement provides a transmission path for vibration between the respective actuators. In FIG. 1, path arrows 9 stylistically depict the paths for vibrational force from the upper actuator into the lower actuator. When vibration occurs in the upper actuator, for instance, it may travel through the upper sleeve 5 and the bearings 4 into the common shaft 1 and the separation maintainer 3 (in embodiments where one is used), and from these into the lower bearings 4 and sleeve 5 of the lower actuator. In this manner, vibration occurring in one actuator has a continuous transmission path to any other actuators mounted on the common shaft 1.
In practice, since both the upper and lower actuators move separately, vibration can be generated in both and interact complexly to effect actuator-mounted device operation, such as that of data read/write heads. It should also be appreciated that vibration inherently has time and frequency related components. Vibrational energy present at a first instant in time may be stored, somewhat, and have an effect at a later second instant in time. Vibrational energy may also be generated, transferred, and absorbed differently depending upon its frequency and its relationship to the resonant and harmonic frequencies of the physical structures which are present.
This can cause particularly undesirable results. For example, a common use of multiple actuators is to separate track following and seeking functions in a magnetic disk storage device such as a computer hard drive. Vibrations occurring in the seeking actuator can travel to the tracking actuator and can cause heads mounted on it to go off course. Alternately, vibrations from the tracking actuator can cause an increase in the settle time for the seeking actuator. Or vibrations created in an actuator at one instant can travel outward, elsewhere into the entire storage assembly, and be reflected back at a later time to adversely effect the operation of the same actuator.
The preceding is not an exhaustive list of all possible vibro-mechanical interactions, but it is enough to demonstrate that disk storage devices are quite complex structures and that designers of them do not have an easy task. If disk storage device design is to continue to evolve, using increasing numbers of mechanical subassemblies operating separately and in concert at increasing speeds, systems are sorely needed for vibration control. Accordingly, an object of the present invention is to provide apparatus and method for vibration control between multiple actuators in disk storage devices. Other objects and advantages will become apparent from the following disclosure.
The present invention relates to split shaft assemblies for vibration control between multiple actuator pivots in a disk storage device. A first actuator pivot is mounted on a first shaft unit and a second actuator pivot is mounted on a second shaft unit. The second shaft unit is mated to the first shaft unit in axial alignment along a common pivot axis by a separating portion of a vibration control material, which interrupts transmission of vibrational force between the first actuator pivot and the second actuator pivot.
A more through disclosure of the present invention is presented in the detailed description which follows and the accompanying figures.